For many reasons, such as concerns for global warming caused by human activity, the increasing cost and potential eventual lack of availability of oil and natural gas, even the shortage of water for hydroelectric power, there is great interest in cost-effective methods and materials for providing energy. Much focus is brought to bear on renewable energy sources, especially upon electricity generated using photovoltaic panels. At the present time the widespread use and installation of electric capacity from solar equipment is hampered by many factors. Present solutions suffer from poor efficiency, short product lifetimes, a poor business model, consumer resistance to a substantial up-front cost that may not be recovered if the consumer does not continue living in a facility equipped with solar equipment long enough to recoup the capital costs.
Efficiency, or lack of it, is primary in these problems. For example, referring to FIG. 1, the current state of the art provides a number of solar panels configured in a series arrangement, the power from the panels then converted from direct current to alternating current. However the efficiency of the sting of panels is dramatically degraded by diminished output by any one of the series-connected panels. Sources of diminished output range from bird droppings to shade or partial shade of a portion of the series of panels from overhanging trees.
FIG. 2 is an example of grid-connected photovoltaic systems, wherein the power provided by the solar system is driven into the grid system of a utility. A representative configuration of a system according to the prior art 202 shows a plurality of panels with a single inverter for converting the direct current provided by the panels in to alternating current electrical power. A representation of an example embodiment of the present invention is shown as system 204. Note that each panel of 204 includes a converter.
Installation costs are high, in part due to the weight of panels and their ancillary structure requirements. In addition, installing panels can be dangerous because the high voltage DC circuit formed as each panel is connected in series is energized whenever illumination is available to the panels. The weight and the safety factors lead to a crew of at least two persons to perform an installation.
In the present art, the use of a centralized inverter forces a separation between the solar panels and the inverter. In most cases this separation is a considerable distance; many feet. Because the principle source of power loss in transmitting DC power over conductors is the current squared times the resistance of the conductor, and low resistance conductors are costly and difficult to work with, high DC voltage is preferred when centralized inverters are used. One way to achieve high DC voltages is to arrange the solar panels in series. This means that the solar panel at the high voltage end of the string has all of its internal circuitry at high voltage, typically several hundred volts and in some cases nearly one thousand volts. To prevent death, injury, arcing and fire the internal circuitry of such a panel must be well insulated. A preferred insulation material is glass, which can contribute substantial cost and weight to the solar panel. The present invention maintains the internal photovoltaic of its associated solar panel near the potential of neutral. In many embodiments no part of the internal set of photovoltaic diodes is more than a few tens of volts away from neutral, which is very close to ground potential. The high voltage portion of an array converter is physically very small, comprising a few square inches, and is typically physically located on the back of a solar panel assembly. This arrangement makes insulation simple and light weight as compared to the prior art modules, which must insulate many square feet on the front of assembly to withstand hundreds of volts.
Solar panels are expected by their makers to last at least twenty five years. However the inverters used in today's installations require very large, high capacitance electrolytic capacitors. These capacitors suffer from temperature extremes, their lifetime particularly shortened by high temperature, such as that experienced on a roof. The liquid in these capacitors will eventually leak out of their canisters, and must be replaced in as little as five years by an experienced technician. This leads to an increased lifetime total cost of ownership. An example circuit including an electrolytic capacitor 302 is shown in FIG. 3.
Even after installation, safety is a concern. Solar panels have no means for disablement; in the event of a fire or tornado or other disaster they can become dangerous. For example, firefighters often find that their best access to a fire is through the roof, so they often chop a hole in it. If a firefighter should penetrate a solar panel or its associated wiring, with a fire axe, especially if he or the axe also comes in contact with ground potential, the result could be lethal.
What is needed is the means to improve efficiency, extend total system lifetime, encourage a business model that lowers the cost of acquisition to consumers, and provides components of a system that can be handled safely during and after installation.